The present invention relates to a probe that senses a level in a process vessel and provides an output indicating the level.
Explosion proof transmitter housings and explosion proof enclosures for other process control equipment are known, but only having explosion proof housings does not complete the explosion proof installation when a probe forms part of the assembly. Both the housing or enclosure and the probe assembly itself must be approved for use in hazardous location installations. Direct mounted probes, that is, probes mounted directly to a housing, require a seal between the probe and the interior of the housing that is adequate to comply with the design requirements. In order to comply with the National Electric Code, an explosion proof barrier has to be located adjacent the housing or such a barrier has to be provided for the probe.
Various attempts have been made to provide seals that will meet the necessary requirements for explosion proof probes under the National Electric Code (NEC) and corresponding codes in other areas, but these are difficult to service and handle and generally cannot be sold as "factory sealed", which is a great benefit in installation.